System and method for controlling automated page-based tier management in storage systems

ABSTRACT

The system includes host computers, file servers and a storage system having automated page-based management means. The storage system interface receives instructions to change the condition for decision for migration regarding particular parts or the whole volume. The host computer can control execution of the migration performed by the storage system by specifying areas or volumes with the condition via the interface. Highly optimized, appropriate data placement and data relocation in computer system can be achieved when the application, host computer or management computer can recognize or predict the usage of the data or files. The storage system having automated page-based management may include compression/decompression and a control method for the compression and decompression process.

CROSS-REFERENCES

This application is a continuation application of U.S. Ser. No.15/198,402, filed Jun. 30, 2016, which is a continuation application ofU.S. Ser. No. 14/174,970, filed Feb. 7, 2014 (now U.S. Pat. No.9,411,716), which is a continuation application of U.S. Ser. No.13/727,727, filed Dec. 27, 2012 (now U.S. Pat. No. 8,688,941), which isa continuation application of U.S. Ser. No. 12/237,204, filed Sep. 24,2008 (now U.S. Pat. No. 8,359,444). The entire disclosures of theseapplications are hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates in general to methods and systems for providingstorage to information systems and, more particularly, to controllingautomated page-based tier management in storage systems.

DESCRIPTION OF THE RELATED ART

Hierarchical storage management also called tier management is a storagemanagement method designed for improving utilization of storageresources in computer systems. Specifically, the utilization ofresources is optimized by changing the location of data in a computersystem based on the value and usage of the data in the enterprise. Onthe other hand, the analysis and classification of the aforesaid valueand the usage are generally difficult tasks. Therefore, recently somestorage system vendors proposed automated page-based hierarchicalstorage management performed by the storage system itself. With thisfunction, the storage system itself monitors access characteristics ofeach small data storage area, such as a page, in a data storage volume,or a file system region, and automatically relocates the data in thepage based on the detected access characteristics. The data relocationis performed regardless of the usage of the data in the host orapplication side.

For example, U.S. Patent Application Publication Number 2006/0010169, toKitamura, incorporated herein by reference, discloses a hierarchicalfile storage management performed by a file server, which is achieved bymeans of page relocation capability of the storage system. In addition,Compellent Technologies, Inc. provides storage system products havingthe automated page-based management or automated tier managementcapability mentioned above. A description of such storage products maybe found athttp://www.compellent.com/Products/Software/Automated-Tiered-Storage.aspx.

The above automated page-based management solves the difficulty of usingconventional hierarchical storage management by avoiding the need toclassify the data or the files. However, in some situations, thisprocess, which is performed automatically by the storage system, failsto achieve the optimal data relocation result because it ignores theactual usage of the data by the user application, even if, in somecases, the application, host computer or management computer canrecognize or predict the usage of the data or files.

SUMMARY OF THE INVENTION

Therefore, there is a need for a method and apparatus to control theautomated page-based management function performed by storage systemaccording to the actual usage of the stored data or files by theapplication or the host computer. Therefore, the inventive methodologyis directed to methods and systems that substantially obviate one ormore of the above and other problems associated with conventionaltechniques by controlling the automated page-based management of storagesystems.

In accordance with one aspect of the inventive methodology, there isprovided a computerized storage system including a computer and astorage system operatively coupled to the computer. The storage systemincorporates at least one storage device configured to store data in atleast one data storage volume, the data storage volume having a firsttier segment and a second tier segment, and a storage controller, thestorage controller including a data migration module configured toautomatically migrate a data unit between the first tier segment and thesecond tier segment in accordance with data usage based on at least onemigration condition. The storage controller of the inventive systemfurther includes an interface configured to enable a change of the atleast one migration condition with respect to at least a part of thedata stored in the data storage volume.

In accordance with another aspect of the inventive methodology, there isprovided a computer-implemented method performed in a computerizedstorage system including a computer; and a storage system operativelycoupled to the computer. The storage system incorporates at least onestorage device configured to store data in at least one data storagevolume, which includes a first tier segment and a second tier segment.The inventive method involves automatically migrating a data unitbetween the first tier segment and the second tier segment in accordancewith data usage based on at least one migration condition and enabling achange of the at least one migration condition with respect to at leasta part of the data stored in the data storage volume.

Additional aspects related to the invention will be set forth in part inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. Aspects ofthe invention may be realized and attained by means of the elements andcombinations of various elements and aspects particularly pointed out inthe following detailed description and the appended claims.

It is to be understood that both the foregoing and the followingdescriptions are exemplary and explanatory only and are not intended tolimit the claimed invention or application thereof in any mannerwhatsoever.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification exemplify the embodiments of the presentinvention and, together with the description, serve to explain andillustrate principles of the inventive technique. Specifically:

FIG. 1 shows a system configuration according to aspects of the presentinvention pertaining to a first embodiment.

FIG. 2 shows an overview of a method of providing volumes, according toaspects of the present invention pertaining to the first embodiment.

FIG. 3 shows an exemplary structure and method for providing thinprovisioned volumes, according to aspects of the present inventionpertaining to the first embodiment.

FIG. 4 shows an exemplary mapping information table, according toaspects of the present invention pertaining to the first embodiment.

FIG. 5 shows an exemplary pool information table, according to aspectsof the present invention pertaining to the first embodiment.

FIG. 6 shows a flowchart of an exemplary control method, according toaspects of the present invention pertaining to the first embodiment.

FIG. 7, FIG. 8 and FIG. 9 show three examples of data usage policyinformation, according to aspects of the present invention pertaining tothe first embodiment.

FIG. 10 shows an exemplary data structure of file system.

FIG. 11 shows a flowchart of an exemplary write process for the TPV,according to aspects of the present invention pertaining to the firstembodiment.

FIG. 12 shows a flowchart of an exemplary read process for the TPV,according to aspects of the present invention pertaining to the firstembodiment.

FIG. 13 shows an example of access information according to aspects ofthe present invention pertaining to the first embodiment.

FIG. 14 shows an example of migration condition information according toaspects of the present invention pertaining to the first embodiment.

FIG. 15 shows an example of page information according to aspects of thepresent invention pertaining to the first embodiment.

FIG. 16 shows an example of volume information according to aspects ofthe present invention pertaining to the first embodiment.

FIG. 17 shows an exemplary flowchart of a process of migration decision,according to aspects of the present invention pertaining to the firstembodiment.

FIG. 18, FIG. 19, FIG. 20 and FIG. 21 show flowcharts of exemplaryprocesses for changing the information regarding the migration decisionprocess of FIG. 17.

FIG. 18 shows a flowchart of an exemplary process for changing migrationsettings for a volume, according to aspects of the present inventionpertaining to the first embodiment.

FIG. 19 shows a flowchart for an exemplary process of setting adjustmentvalues in volume information, according to aspects of the presentinvention pertaining to the first embodiment.

FIG. 20 shows a flowchart of an exemplary process for changing migrationsettings for a segment, according to aspects of the present inventionpertaining to the first embodiment pertaining to the first embodiment.

FIG. 21 shows a flowchart for an exemplary process of setting adjustmentvalues in page or segment information, according to aspects of thepresent invention pertaining to the first embodiment.

FIG. 22 shows a flowchart of an exemplary migration process according toaspects of the present invention pertaining to the first embodiment.

FIG. 23 shows exemplary migration information according to aspects ofthe present invention pertaining to the first embodiment.

FIG. 24 shows another exemplary system configuration according toaspects of the present invention pertaining to the first embodiment.

FIG. 25 shows yet another system configuration according to aspects ofthe present invention pertaining to the first embodiment.

FIG. 26 shows a system configuration according to aspects of the presentinvention pertaining to a second embodiment.

FIG. 27 shows an exemplary mapping information for use with the systemconfiguration according to the second embodiment of the presentinvention.

FIG. 28 shows an exemplary pool information for use with the systemconfiguration according to the second embodiment of the presentinvention.

FIG. 29 shows compression/decompression capability in migration betweenhigher tier and lower tier.

FIG. 30, FIG. 31 and FIG. 32 show three exemplary methods for processingdata with compression/decompression for page-based tier management andwrite access according to the second embodiment of the presentinvention.

FIG. 33 shows an exemplary mapping information corresponding to themethod of FIG. 32, according to the second embodiment of the presentinvention.

FIG. 34 and FIG. 35 show exemplary page information and volumeinformation according to the second embodiment of the present invention.

FIG. 36 shows a flowchart for a process of changing informationpertaining to compression in migration according to the secondembodiment of the present invention.

FIG. 37 shows an exemplary embodiment of a computer platform upon whichthe inventive system may be implemented.

DETAILED DESCRIPTION

In the following detailed description, reference will be made to theaccompanying drawing(s), in which identical functional elements aredesignated with like numerals. The aforementioned accompanying drawingsshow by way of illustration, and not by way of limitation, specificembodiments and implementations consistent with principles of thepresent invention. These implementations are described in sufficientdetail to enable those skilled in the art to practice the invention andit is to be understood that other implementations may be utilized andthat structural changes and/or substitutions of various elements may bemade without departing from the scope and spirit of present invention.The following detailed description is, therefore, not to be construed ina limited sense. Additionally, the various embodiments of the inventionas described may be implemented in the form of a software running on ageneral purpose computer, in the form of a specialized hardware, orcombination of software and hardware.

Aspects of the present invention provide systems and methods forcontrolling automated page-based migration in storage system.

FIG. 1 shows an exemplary system configuration according to aspects ofthe present invention pertaining to a first embodiment of the inventivemethodology. The storage system of FIG. 1 may include some or all of thefollowing components: storage system 100, storage controller 110, mainprocessor 111, switch 112, host interface 113, memory 200, cache 300,disk controller 400, storage disk 600 such as hard disk drive (HDD), andbackend path 601, which can be implemented using a variety ofinterconnect technologies, including Fibre Channel, SATA, SAS,iSCSI(IP), or the like. In an embodiment of the invention, the storagedisk 600 and disk controller 400 can replaced by Solid State Device suchas flash memory and a controller controlling them.

The main processor 101 executes various processes necessary for theoperation of the storage controller 100. The main processor 101 andother components use the following information stored in the memory 200:mapping information 201, pool information 202, page information 203,volume information 204, access information 205, migration condition 206,and migration information 207.

The main processor 101 performs the aforesaid processes by executing thefollowing programs stored in the memory 200. The programs stored in thememory 200 include a read process program 211, a write process program212, a migration decision program 213 and a data migration program 214.The details of these programs will be described in detail below.

The file servers 510 are coupled to the host interface 113 via SAN 900that may be implemented using various types of technologies, includingFibre Channel, iSCSI(IP) or the like. The host 500, file server 510 andstorage controller 110 are coupled each other via LAN 902, which may beimplemented as an IP network.

Volumes, namely logical units (LUs), provided by the storage system 100,are composed from collection of physical storage areas in the HDDs. Theintegrity of the data stored in those areas may be protected by means ofa stored parity code, such as in RAID configuration, well known topersons of skill in the art.

In addition to the file system 501 and the OS 502, the host 500 storesan application program 503, a data management program 504 and data usagepolicy information 505. To execute these programs, the host 500 alsoincorporates resources such as a processor, memory, and storage devices,which are not shown in FIG. 1. The details of these programs will bedescribed in detail below. The file server 510 includes a file system511, OS 502, file service program 513 and migration management program514. To properly execute these programs, the file server 510 alsoincludes resources such as processer, memory and storage devices, whichare not shown in FIG. 1. The details of these programs will be describedin detail below.

FIG. 2 shows an overview of an exemplary method for provisioning andusing data volumes in the storage system 100. The storage system 100provides thin provisioned volumes (TPV) 610 as a data storage area forthe file server 510. The file server 510 performs read and write accessoperations to use and store the data in the TPV 610 via the SAN 900,while the host computer 500 performs various file access operationsincluding read and write operations with respect to the files managed bythe file server 510 via the LAN 902. The file server 510 processes therequests from the host computers 500 by using the file service program513.

FIG. 3 shows an exemplary structure and method for providing thinprovisioned volumes, according to aspects of the present inventionpertaining to the first embodiment. The storage system 100 includes poolvolumes 620 and subdivides the pool volumes 620 into a number offixed-length areas called chunks 690. The storage system 100 assigns achunk 690 to a segment of a virtual volume or a TPV 610 at the time awrite access to the target segment is performed. In other words, thephysical storage area is assigned on demand. In FIG. 3, the TPV 610virtually includes multiple segments and a chunk 690 is allocated fromthe pool volume 620 and assigned to the appropriate segment. A segmentis a fixed length area or a page of the TPV. For example, the chunk 4 isassigned to the segment 6 as shown in FIG. 3. That is, a TPV 610 is apage-based volume.

To achieve assignment of chunks to segments of the TPV, the storagecontroller 110 uses mapping information 201 (FIG. 4) and poolinformation 202 (FIG. 5). FIG. 4 is an example of mapping information201. This information maintains mapping between chunks and segments ofeach volume. Status of assignation is ‘No’ if no chunk is assigned tothe segment. The tier that the segment belongs to at that time isindicated in ‘Tier’ section. A usage of flag of “under migration” isdescribed later. This information can be constructed as a list or adirectory of each element for faster search.

FIG. 5 shows an exemplary pool information table, according to aspectsof the present invention pertaining to the first embodiment. The poolinformation 202 is used to manage and determine whether a chunk is usedor not. By using this information, the storage controller 110 is able tofind free (unused) chunks in the write process described below. The tierthat the chunk belongs to at that time is indicated in the ‘Tier’section. This information can also be constructed as a list or directoryof each element for faster search of a free chunk.

As shown in U.S. Patent Publication No. 2006/0010169, incorporatedherein by reference, the storage system 100 can realize page-basedtransparent data migration between chunks by copying data and changingthe mapping information 201. As described below, the page-basedtransparent migration mentioned above is managed by the storage system100 itself by way of an automated tier management. However, according toaspects of the present invention, the host 500 can control thismanagement process according to the data usage policy of the host 500.

FIG. 6 shows a flowchart of an exemplary control method, according toaspects of the present invention pertaining to the first embodiment. Theprocess begins at 1000. At 1001, the host 500 checks the current datausage policy information 505. This information is set by user orgenerated by the host 500 itself as information showing a plan orforecast of usage of the data or file.

At 1002, if there are one or more files that have necessity to changesetting regarding migration performed by the storage system 100, theprocess proceeds to 1003. Otherwise, the process terminates at 1006.

At 1003, the host 500 instructs the file server 510 to change thesetting with respect to the migration of the data or the file performedby the storage system 100 with respect to the target file.

At 1004, the file server 510 obtains the location of the data in the TPV610 corresponding to the specified file. FIG. 10 shows an example offile system data structure. Each INODE in FIG. 10 can be used toindicate a file or directory. The INODE indicates a file when its FILETYPE field is “file” such as 804 and 807. If the INODE indicates a file,then the data blocks pointed from block pointer in the INODE containactual data of the file. If a file is stored in a plurality of datablocks, for example in 10 blocks, the addresses of the 10 data blocksare recorded in block pointer. The INODE indicates a directory if theFILE TYPE field is “directory” such as 801 and 803. If the INODEindicates a directory, then the data blocks pointed from block pointerin the INODE stores the list of INODE numbers and names of all files anddirectories that reside in the directory. This list is called directoryentry. These types of information used to manage files are stored involumes in the storage system 100 according to a predetermined placementrule. Therefore, the file sever 510 can obtain information on thelocation of the data by tracing such information stored in the TPV 610.

At 1005, the file server 510 changes the setting by instructing thestorage system 100 to change the location of the data and specifies thetarget location. The process performed in the storage system 100 inresponse to this request is described below.

There are several situations when the host 500 should control the tiermanagement performed by the storage system 100. These situations arerelated to usage policy offered by the application or the user. Examplesof these situations will be described below.

As would be appreciated by those of skill in the art, the priority orrequired service level of data is determined by the host 500. In thiscase, the host 500 can control or suggest appropriate relocation of thedata or the file using a recognized projection of the specifics of thedata utilization.

FIG. 7, FIG. 8 and FIG. 9 show three examples of data usage policyinformation, according to aspects of the present invention pertaining tothe first embodiment. Specifically, FIG. 7 illustrates an example of thedata usage policy information 505 that resides on the host computer 500.In this example, type, expected service level and expected latency ofeach file at a particular time are maintained and updated by theapplication program 503 or by the user, if necessary. Therefore, thedata management program 504 can suggest a setting for relocation byreferring to the information 505 at each point in time.

FIG. 8 shows another example of the data usage policy information 505.In this example, the data are arranged by project ID and files used ineach project performed by the host 500 are shown. For each project ID,expected service level and planned or forecasted duration of the projectare also shown. By referring to the information in the table of FIG. 8,the host 500 can recognize usage and requirements of the files in thefuture and make a suggestion for data or file relocation.

FIG. 9 shows yet another example of data usage policy information 505.In this example, expected service level and latency of each file arepresented together with the respective term, which can be based on aplan or a forecast.

As another example of the situation when the host 500 should control thetier management performed by the storage system 100, the data isrelocated by means other than the storage system 100. An example of asystem configuration where a file server 510 includes a file migrationprogram 515 is shown in FIG. 25.

FIG. 25 shows an example of an alternative system configuration where afile server 510 additionally includes a file migration program 515. Withthis system configuration, a file can be relocated by the file server510 instead of the storage system 100 when the migration is performeddirectly, when multiple files are relocated simultaneously or when anentire database file is relocated simultaneously. Moreover, the fileserver 510 can relocate a file even if migration among the storagesystems 100 is required. The alternative configuration of FIG. 25permits the data to be relocated by means other than the storage system100. In this situation, it is preferable that tier management of thestorage system 100 can be controlled from the host 500 or the fileserver 510 a.

FIG. 11 shows a flowchart of an exemplary write process for the TPV,according to aspects of the present invention pertaining to the firstembodiment. The process beings at 1100.

At 1101, the file server 510 issues a write request and transfers writedata to the storage controller 110.

At 1102, the storage controller 110 checks the target TPV 610 and targetarea of the write access by referring to the write request.

At 1103, the storage controller 110 checks the mapping information 201for a segment in the target area. If a chunk has already been assignedto the segment, the process proceeds to 1106. Otherwise, the processproceeds to 1104.

At 1104, the storage controller 110 assigns a new chunk to store thewrite data. To do this, the storage controller 110 updates the mappinginformation 201 and the pool information 202. By using the poolinformation 202, the storage controller 110 finds the new chunk from thehighest tier, i.e. tier 1.

At 1105, the storage controller 110 stores the write data to the newchunk. Then, the process proceeds to 1110.

If a chunk has already been assigned to the segment and the process hasproceeded to 1106, at 1106, the storage controller 110 checks ‘undermigration’ flag in the mapping information 201. This flag is set duringthe migration process described later and shows whether the chunk isunder migration or not. If the chunk is under migration, the processproceeds to 1107. Otherwise, the process proceeds to 1109.

At 1107, by referring to the migration information 207 described later,the storage controller 110 checks whether the area pertaining to thewrite command in the chunk has been copied during the migration process.If yes, the process proceeds to 1108. Otherwise, the process proceeds to1109.

At 1108, the storage controller 110 stores the write data at themigration target.

At 1109, the storage controller 110 stores the write data at theexisting chunk.

The process arrives at 1110 after the storage controller 110 stores thewrite data at the current chunk, at either 1105, where a new chunk isassigned, or 1109, where a pre-assigned chunk exists. At 1110, thestorage controller 110 updates the access information 205. This accessinformation records access characteristics of the segment (i.e. page)and is used for determination of migration as described later.

At 1111, if the storage controller 110 has checked all segments of thetarget area, the process ends at 1113. Otherwise, the storage controller110 advances the check to the next segment at 1112.

FIG. 12 shows a flowchart of an exemplary read process for the TPV,according to aspects of the present invention pertaining to the firstembodiment.

An exemplary write process for the TPV 610 begins at 1200.

At 1201, the file server 510 issues a read request to the storagecontroller 110.

At 1202, the storage controller 110 checks the target TPV 610 and targetarea of the read access by referring to the read request.

At 1203, the storage controller 110 checks the mapping information 201for a segment in the target area. If a chunk has already been assignedto the segment, the process proceeds to 1204. Otherwise, the processproceeds to 1206.

At 1204, the storage controller 110 transfers the data stored in thechunk to the file server 510.

At 1205, the storage controller 110 updates the access information 205.

At 1206, the storage controller 110 sends data of zero (0) to the fileserver 510.

At 1207, if the storage controller 110 has checked all segments of thetarget area, the process ends at 1209. Otherwise, the storage controller110 advances the check to the next segment at 1208.

FIG. 13 shows an example of access information according to aspects ofthe present invention pertaining to the first embodiment. Specifically,the access information 205 is stored in the memory 200 of the storagecontroller 110. The access information 205 includes informationregarding access for each segment such as access rate per unit time,last access time and average access length, for each of the read andwrite requests. The information regarding the average access durationmay be initialized at a certain interval. Accordingly, the averageaccess length is reset to an initialized value at regular intervals.

FIG. 14 shows an example of migration condition information according toaspects of the present invention pertaining to the first embodiment.Specifically, FIG. 14 shows an example of the migration conditioninformation 206 that is stored in the memory 200 of the storagecontroller 110. The migration condition information 206 is used by theflowchart of FIG. 17. The migration information maintains conditionsthat determine occurrence of migration for each movement between tiers.The condition may be registered by user via the host 500, the fileserver 510 and/or the management terminal of the storage system 100. Thestorage controller 110 can determine the occurrence of migration byreferring to and comparing the values of the parameters listed in themigration condition information 206 and the conditions.

For example, according to the table shown, a migration type from tier 1to tier 2 occurs if a first condition and a second condition are bothmet. The first condition in this case is an access rate per unit time ofless than 1500 times and the second condition is that the last accesstime occurred before 10 days ago.

FIG. 15 shows an example of page information according to aspects of thepresent invention pertaining to the first embodiment. Specifically, FIG.15 shows an example of the page information 203 located on the memory200 of the storage controller 110. As described later, this informationincludes adjustment values for the determination and a flag showingprohibition of migration for each segment. For each TPV ID, the relevantsegment IDs are listed. For each segment, a flag having values of YES orNO indicates whether migration is prohibited or not. Further, for eachsegment, an adjustment value may be separately provided for read andwrite requests. The adjustment is a function of whether the operation isread or write, access rate per unit time and last access time.

FIG. 16 shows an example of volume information according to aspects ofthe present invention pertaining to the first embodiment. Specifically,FIG. 16 shows an example of the volume information 204 located on thememory 200 of the storage controller 110. As described later, thisinformation includes adjustment values for the determination and a flagshowing prohibition of migration for each volume. This information isorganized similarly to the information of FIG. 15 except that one valuepertains to an entire volume as opposed to having values for eachsegment of a volume.

FIG. 17 shows an exemplary flowchart of a process of migration decision,according to aspects of the present invention pertaining to the firstembodiment. Specifically, the process of FIG. 17 is for determiningwhether or not migration will be performed. During this process thevalues from table 205 are adjusted in accordance with the values intable 203 and subsequently used in comparison to arrive at a decision ofwhether migration of the page should occur and what type of migrationshould take place. The process begins at 1300. At 1301, the storagecontroller 110 chooses a segment (i.e. page) to be examined.

At 1302, the storage controller 110 investigates the page information203 and the volume information 204. FIG. 15 and FIG. 16 show examples ofthe page information 203 and the volume information 204, respectively.As described below, this information includes adjustment values for thedetermination of migration and a flag showing prohibition of migrationfor each segment or volume.

At 1303, if prohibition of migration for the segment or the TPV is setto a YES value, the process ends at 1313. That is, migration is notperformed. If there is no prohibition for migration, the processproceeds to 1304.

At 1304, by referring to the access information 205, the storagecontroller 110 obtains one or more values to be compared with themigration condition information 206.

At 1305, if according to the page information 203 there is adjustmentfor the TPV containing the segment, the process proceeds to 1306.Otherwise, the process proceeds to 1307.

At 1306, the storage controller 110 adjusts the values to be comparedaccording to the adjustment provided in the volume information 204. Thatis, the adjustment value is added to the value to be compared. Theadjustment values are obtained from the page information 203 and areused to modify or adjust the values provided by the access information205. The adjusted or modified values are subsequently used against themigration condition information 206. And then, the process proceeds to1309.

At 1307, if there is adjustment for the segment, the process proceeds to1308. Otherwise, the process proceeds to 1309.

At 1308, the storage controller 110 adjusts the values to be comparedaccording to the adjustment set in the page information 203. And then,the process proceeds to 1309.

At 1309, the storage controller 110 decides whether migration of data inthe segment should be performed according to the conditions provided inthe migration condition information 206. FIG. 14 shows an example ofmigration condition information 206. The storage controller 110 candetermine the type of migration and whether or not migration shouldoccur by comparing the adjusted values such as the access rate per unittime and the last access time with the values provided in the migrationcondition information 206.

At 1310, if the comparison indicates that migration should occur, theprocess proceeds to 1311. Otherwise, the process ends.

At 1311, the storage controller 110 finds the destination of themigration to the suitable tier determined from the conditions of FIG. 14and updates the pool information 202 of FIG. 5.

At 1312, the storage controller 110 performs the migration. The detailedprocess of the migration is described below.

The above migration decision process is repeated at predeterminedintervals or performed when load of the storage system 110 is low. Thisprocess is performed for segments that have stored data.

In examples of page information 203 and volume information 204 shownrespectively in FIG. 15 and FIG. 16, the initial value of theprohibition of migration flag is ‘NO’ indicating that migration is notprohibited. The initial value of adjustments is zero or ‘none’. Thesevalues subsequently change as the updates are performed.

FIG. 18, FIG. 19, FIG. 20 and FIG. 21 show flowcharts of exemplaryprocesses for changing the information regarding the migration decisionprocess of FIG. 17. Specifically, FIG. 18 shows a flowchart of anexemplary process for changing migration settings for a volume,according to aspects of the present invention, pertaining to the firstembodiment.

In FIG. 18, the process occurs in response to the storage controller 110receiving an instruction to change the settings of migration.

At 1400, the process begins.

At 1401, the storage controller 110 receives an instruction to changethe settings applicable to migration. This means that the storage system100 provides an interface (e.g. API) for changing the settings. Asmentioned above, the file server 510, the host 500 and the othercomputers may issue the setting change instruction using the interface.The instruction to change setting can be transferred via the SAN 900and/or the LAN 920 because the interface can be implemented in variousmanners such as a SCSI command on FC and XML on HTTP. That is, thestorage controller 110 may receive the setting change instruction invarious manners.

At 1402, the storage controller 110 inspects the instruction. Theinstruction includes information or parameters that are used for thefollowing steps. In this step, if the instruction is determined to befor a volume, the process proceeds to 1403. Otherwise, the processproceeds to A which leads to 1601 in FIG. 20.

At 1403, if the instruction is to set prohibition of migration, theprocess proceeds to 1404. Otherwise, the process proceeds to 1405.

At 1404, the storage controller 110 sets the flag of prohibition ofmigration for the specified volume in the volume information 204 to‘YES’. After that, the process terminates at 1412.

At 1405, if the instruction is to release the prohibition of migration,the process proceeds to 1406. Otherwise, the process proceeds to 1407.

At 1406, the storage controller 110 sets the flag of prohibition ofmigration for the specified volume in the volume information 204 to‘NO’. There is no prohibition on migration in effect and, after that,the process terminates at 1412.

At 1407, if the instruction is to set adjustments for the volume, theprocess proceeds to 1408. Otherwise, the process proceeds to 1409.

At 1408, the storage controller 110 sets adjustment values for thespecified volume in the volume information 204 according to theinstruction. Setting of the adjustment values is described in detailfurther below. After setting of the adjustments at 1408, the processterminates at 1412.

At 1409, if the instruction is to reset adjustment values, the processproceeds to 1410. Otherwise, the process proceeds to 1411.

At 1410, the storage controller 110 resets adjustment values for thespecified volume in the volume information 204 to initial values. Afterthat, the process terminates at 1412.

At 1411, the storage controller 110 reports an error regarding theinstruction to the sender of the instruction and, after that, theprocess terminates at 1412. The process of FIG. 18 arrives at the errormessage at 1411, if the instructions received pertain to a volume, donot require setting of prohibition of migration, do not require releaseof prohibition of migration, do not require adjustments to theconditions, and do not require resetting of the adjustments. In short,they instruct nothing particular to be done.

FIG. 19 shows a flowchart for an exemplary process of setting adjustmentvalues in volume information, according to aspects of the presentinformation. Specifically, FIG. 19 shows the details of the processperformed in 1408 of FIG. 18 for setting adjustment values in the volumeinformation 204. This process begins at 1500.

At 1501, if the instruction is to set adjustment of read access rate,the process proceeds to 1502. Otherwise, the process proceeds to 1503.

At 1502, the storage controller 110 sets adjustment of read access ratefor the specified volume in the volume information 204 according to theinstruction and the process terminates at 1510.

At 1503, if the instruction is to set adjustment of write access rate,the process proceeds to 1504. Otherwise, the process proceeds to 1505.

At 1504, the storage controller 110 sets adjustment of write access ratefor the specified volume in the volume information 204 according to theinstruction and the process terminates at 1510.

At 1505, if the instruction is to set adjustment of last access time ofread access, the process proceeds to 1506. Otherwise, the processproceeds to 1507.

At 1506, the storage controller 110 sets adjustment of last access timeof read access for the specified volume in the volume information 204according to the instruction and the process terminates at 1510.

At 1507, if the instruction is to set adjustment of access time of writeaccess, the process proceeds to 1508. Otherwise, the process proceeds to1509.

At 1508, the storage controller 110 sets adjustment of last access timeof write access for the specified volume in the volume information 204according to the instruction and the process ends at 1510.

At 1509, the storage controller 110 reports an error regarding theinstruction to the sender of the instruction and the process terminatesat 1510. The process 1408 of FIG. 18 arrives at the error message at1509, if the instruction is not for setting adjustment of read or writeaccess rates, nor for setting adjustment of last access time for read orwrite operations.

FIG. 20 shows a flowchart of an exemplary process for changing migrationsettings for a segment, according to aspects of the present inventionpertaining to the first embodiment. Specifically, FIG. 20 shows thedetails of the process performed after 1402 of FIG. 18 for settingadjustment values in the page information 203. As such, FIG. 20 shows apart of the process to change settings used for migration of FIG. 18.This part is similar to the part shown in FIG. 18 pertaining to volumesexcept that the process shown in FIG. 20 changes the information about aspecified segment, as opposed to a volume.

FIG. 21 shows a flowchart for an exemplary process of setting adjustmentvalues in page or segment information, according to aspects of thepresent information. Specifically, FIG. 21 is the detailed processperformed at 1606 of FIG. 20 and is similar to the process described inFIG. 19 except that it changes the information about the specifiedsegment, not volume. That is, with the process illustrated in FIG. 20and FIG. 21, the page information 203 is changed according to theinstruction received.

With the process described above, the file server 510, the host 500 andthe other computers can change the settings regarding migration fromeither the page or volume perspective. Because these settings affectsthe decision regarding migration, computers such as the host 500 areprovided with a method to control automated page-based management ortier management performed by the storage system 100.

As another example of setting change instruction and process, pluralsettings can be changed by one instruction.

FIG. 22 shows a flowchart of an exemplary migration process according toaspects of the present invention pertaining to the first embodiment.FIG. 23 shows exemplary migration information according to aspects ofthe present invention pertaining to the first embodiment.

Specifically, FIG. 22 illustrates the migration process performed in1312 of FIG. 17. FIG. 23 shows an example of the migration information207. Migration information 207 includes ID of the segment to be moved,information regarding the unused location selected as destination andcopy pointer that denotes progress of copy.

The process of migration begins at 1800. At 1801, storage controller 110makes an entry in migration information 207 for the segment to be moved.The storage controller 110 also sets a flag of “under migration” for thesegment in the mapping information 201 to ‘YES’.

At 1802, the storage controller 110 copies data in the segment to alocation selected as destination. According to progress of the copying,copy pointer in the migration information 207 is updated and movesforward.

At 1803, after completion of the copying, the storage controller 110updates the mapping information 201 to change mapping between thesegment and physical location according to the migration. This realizesthe transparent migration of the segment for the host 500.

At 1804, the storage controller 110 updates the pool information 202 torelease the chunk that was being used by the segment if no segment iscurrently using the chunk.

At 1805, the storage controller 110 deletes the entry in the migrationinformation 207 and updates the mapping information 201 to set the flagof “under migration” for the segment to ‘NO.’

At 1806, the migration process terminates.

FIG. 24 shows another exemplary system configuration according toaspects of the present invention pertaining to the first embodiment. Inthe alternative configuration of FIG. 24, the hosts 500 are coupled tothe host interface 113 of the storage controller 100 via the SAN 900.The connection may be through Fibre Channel or iSCSI(IP). In otherwords, in the system of FIG. 24 there is a SAN-type coupling between thehost 500 and the storage system 100 whereas in FIG. 1, only the fileserver 510 was coupled to the storage system 100 via the SAN 900.

In the previous configuration shown in FIG. 1, the host 500 controls theautomated page-based management performed by the storage system 100 viathe file server 510 because the file server manages and recognizelocation of each file (i.e. data). However the host 500 also canrecognize the location of data when the host 500 handles the data withraw access or block access. In other words, the host 500 can store thedata in the TPV 610 provided by the storage system 100 with block accessand can know the location of the data in the TPV 610.

Therefore with the configuration shown in FIG. 24, in order to controlautomated page-based management in the storage system 100, the host 500instructs the storage system 100 to change settings regarding migrationvia the SAN 900 and/or the LAN 902 directly. Moreover, other type ofcomputers such as a management server also can control the storagesystem 100 through the SAN 900 and/or the LAN 902.

FIG. 26 shows a system configuration according to aspects of the presentinvention pertaining to a second embodiment. FIG. 27 shows an exemplarymapping information 201 for use with the system configuration accordingto the second embodiment of the present invention. FIG. 28 shows anexemplary pool information 202 for use with the system configurationaccording to the second embodiment of the present invention.

In the system of FIG. 26, a storage controller 110 a includes acompression/decompression processor 114. With thecompression/decompression processer 114, the storage controller 110 acan compress and decompress data stored in a storage system 100 a,especially for migration between tiers. As shown in FIG. 29, the datarelocated to a lower tier is compressed in order to achieve moreeffective use of capacity. This realizes advanced tier managementbecause compression of lower tire improves capacity cost by virtualexpansion of capacity.

Data to be compressed should be selected or screened because compressionand decompression causes overhead, load and latency in the process ofthe storage system 100 a. In other words, control of tier managementwith compression is desired. For example, data that requires relativelyhigh service level, even if in a lower tier, should not be compressed.As another example, some types of files such as JPEG files and MPEGfiles should not be compressed because a file of these types generallydoes not achieve large reduction of size with compression.

As shown in FIG. 29, in a compressed lower tier, one chunk (e.g. ChunkA) may have data of multiple segments (e.g. Data A, Data B and Data C).In order to manage such a relationship, an exemplary of mappinginformation 201 shown in FIG. 27 includes information regarding startaddress in a chunk and length of each segment. Moreover, an exemplarypool information 202 shown in FIG. 28 has information about number ofsegments in each chunk and ID information of each segment included achunk. The mapping information 201 also includes information indicatingwhether the segment has been compressed or not.

FIG. 30, FIG. 31 and FIG. 32 show three exemplary methods for processingdata with compression/decompression for page-based tier management andwrite access according to second embodiment of the present invention.

Specifically, FIG. 30 illustrates one example of the data processingmethod with compression and decompression. In FIG. 30, the storagecontroller 110 does not store data of one segment in two or more chunksbeyond the edge of a chunk. In other words, each segment goes to onechunk and is not divided between chunks. One chunk may include data frommultiple segments but data of none of the segments goes beyond the chunkto the next chunk. Moreover, if one chunk has data of multiple segments,the storage controller 110 decompresses just data of the segment to bemoved to higher tier and relocates it while leaving other data stillcompressed in the chunk when the migration happens.

FIG. 31 illustrates another example of the data processing method withcompression and decompression. In FIG. 31, the storage controller 110again does not store data of one segment in two or more chunks beyondedge of a chunk. However, in this example, if one chunk has data ofmultiple segments, the storage controller 110 a decompresses data of allsegments in the chunk and relocates them when the migration of data inthe chunk happens. Therefore the chunk becomes unused immediately andcan be released at the point in time.

FIG. 32 illustrates yet another example of the data processing methodwith compression and decompression. In FIG. 32, unlike the previous twomethods, the storage controller 110 may divide data of one segment andmay store the data in two chunks beyond edge of the chunks. If one chunkhas data of multiple segments, the storage controller 110 decompressesjust data of segment to be moved to the higher chunk and relocates thisdata while leaving the other data compressed and remaining in the chunkwhen the migration happens. This method avoids wasting storage capacityof chunks.

FIG. 33 shows an exemplary mapping information 201 for the method ofFIG. 32 according to the second embodiment of the present invention. Inaddition to information regarding the number of chunks for each segment,with this mapping information, the same segment can have multiplelocations in multiple chunks.

FIG. 34 and FIG. 35 show exemplary page information and volumeinformation according to the second embodiment of the present invention.As mentioned above, it should be controlled whether data of one segment(or volume) is compressed or not. FIG. 34 and FIG. 35 show examples ofpage information 203 and volume information 204 for the secondembodiment. These information are similar to the page information 203and volume information 204 described for the first embodiment of FIG. 1,except that each of 203 and 204 includes a flag of prohibition ofcompression. The initial value of the flag is ‘NO.’ This flag can bechanged according to a process described below with respect to FIG. 36.

FIG. 36 shows a flowchart for a process of changing informationpertaining to compression in migration according to the secondembodiment of the present invention. The process begins at 1900. At1901, the storage controller 110 receives an instruction to changesetting of migration. This means that the storage system 100 provides aninterface (e.g. API) for changing the setting. As mentioned above, thefile server 510, the host 500 and other computers issue the instructionusing the interface. The instruction can be transferred via SAN 900and/or LAN 920 since the interface can be implemented in various mannerssuch as SCSI command on FC and XML on HTTP. That is, the storagecontroller 110 may receive the instruction in various manners.

At 1902, the storage controller 110 checks the instruction. Theinstruction includes information or parameters mentioned in thefollowing decision steps of this process. In this step, if theinstruction is about compression, the process proceeds to 1904.Otherwise, the process proceeds to 1903.

At 1903, the storage controller 110 performs the process of prohibitionof migration or adjustment for migration described in FIG. 18, FIG. 19,FIG. 20 and FIG. 21 and, after that, the process terminates at 1913.

At 1904, if the instruction is to set prohibition of compression for thevolume, the process proceeds to 1905. Otherwise, the process proceeds to1906.

At 1905, the storage controller 110 sets a flag of prohibition ofcompression for the specified volume in volume information 204 to ‘YES’and then the process terminates at 1913.

At 1906, if the instruction is to stop prohibition of compression forthe volume, the process proceeds to 1907. Otherwise, the processproceeds to 1908.

At 1907, the storage controller 110 sets a flag of prohibition ofcompression for the specified volume in volume information 204 to ‘NO’and then the process terminates at 1913.

At 1908, if the instruction is to set prohibition of compression forsegment, the process proceeds to 1909. Otherwise, the process proceedsto 1910.

At 1909, the storage controller 110 sets a flag of prohibition ofcompression for the specified segment in page information 203 to ‘Yes’and then the process terminates at 1913.

At 1910, if the instruction is to stop prohibition of compression forsegment, the process proceeds to 1911. Otherwise, the process proceedsto 1912.

At 1911, the storage controller 110 sets a flag of prohibition ofcompression for the specified segment in page information 203 to ‘NO’and then the process ends.

At 1912, the storage controller 110 reports an error regarding theinstruction to the sender of the instruction and, after that, theprocess terminates at 1913.

Migration decision process and migration process of this embodiment aresimilar to the processes described with respect to the first embodiment.In this embodiment, in step 1311 of FIG. 17, the storage controller 110refers to a flag of prohibition of compression in the page information203 for the segment to be relocated and a flag of prohibition ofcompression in the volume information 204 for the volume having thechunk, before selecting the destination. Then, the storage controller110 chooses the destination according to the result of the checking ofthe flags. With regard to the migration process following the decision,in step 1802 of FIG. 22, the storage controller 110 copies data withcompressing or decompressing the data if compression or decompression isneeded. As mentioned above, this compression/decompression capabilitycan achieve better per capacity cost in tiered storage managementbecause of virtual expansion of capacity.

As example of method to use the compression/decompression capability,application of the capability may be selectable. That is, application ofcompression to lower tier is selected by user initially, and then, thesetting control mentioned above can be applied.

By applying the processes described in the above embodiments, highlyoptimized, appropriate data placement and data relocation in thecomputer system are realized because computers such as the host 500, thefile server 510 and the management server can control the storagesystem's 100 automated page-based management from their own perspectivewith their own information such as data usage policy and applicationinformation.

FIG. 37 is a block diagram that illustrates an embodiment of acomputer/server system 3700 upon which an embodiment of the inventivemethodology may be implemented. The system 3700 includes acomputer/server platform 3701, peripheral devices 3702 and networkresources 3703.

The computer platform 3701 may include a data bus 3704 or othercommunication mechanism for communicating information across and amongvarious parts of the computer platform 3701, and a processor 3705coupled with bus 3701 for processing information and performing othercomputational and control tasks. Computer platform 3701 also includes avolatile storage 3706, such as a random access memory (RAM) or otherdynamic storage device, coupled to bus 3704 for storing variousinformation as well as instructions to be executed by processor 3705.The volatile storage 3706 also may be used for storing temporaryvariables or other intermediate information during execution ofinstructions by processor 3705. Computer platform 3701 may furtherinclude a read only memory (ROM or EPROM) 3707 or other static storagedevice coupled to bus 3704 for storing static information andinstructions for processor 3705, such as basic input-output system(BIOS), as well as various system configuration parameters. A persistentstorage device 3708, such as a magnetic disk, optical disk, orsolid-state flash memory device is provided and coupled to bus 3701 forstoring information and instructions.

Computer platform 3701 may be coupled via bus 3704 to a display 3709,such as a cathode ray tube (CRT), plasma display, or a liquid crystaldisplay (LCD), for displaying information to a system administrator oruser of the computer platform 3701. An input device 3710, includingalphanumeric and other keys, is coupled to bus 3701 for communicatinginformation and command selections to processor 3705. Another type ofuser input device is cursor control device 3711, such as a mouse, atrackball, or cursor direction keys for communicating directioninformation and command selections to processor 3704 and for controllingcursor movement on display 3709. This input device typically has twodegrees of freedom in two axes, a first axis (e.g., x) and a second axis(e.g., y), that allows the device to specify positions in a plane.

An external storage device 3712 may be coupled to the computer platform3701 via bus 3704 to provide an extra or removable storage capacity forthe computer platform 3701. In an embodiment of the computer system3700, the external removable storage device 3712 may be used tofacilitate exchange of data with other computer systems.

The invention is related to the use of computer system 3700 forimplementing the techniques described herein. In an embodiment, theinventive system may reside on a machine such as computer platform 3701.According to one embodiment of the invention, the techniques describedherein are performed by computer system 3700 in response to processor3705 executing one or more sequences of one or more instructionscontained in the volatile memory 3706. Such instructions may be readinto volatile memory 3706 from another computer-readable medium, such aspersistent storage device 3708. Execution of the sequences ofinstructions contained in the volatile memory 3706 causes processor 3705to perform the process steps described herein. In alternativeembodiments, hard-wired circuitry may be used in place of or incombination with software instructions to implement the invention. Thus,embodiments of the invention are not limited to any specific combinationof hardware circuitry and software.

The term “computer-readable medium” as used herein refers to any mediumthat participates in providing instructions to processor 3705 forexecution. The computer-readable medium is just one example of amachine-readable medium, which may carry instructions for implementingany of the methods and/or techniques described herein. Such a medium maytake many forms, including but not limited to, non-volatile media,volatile media. Non-volatile media includes, for example, optical ormagnetic disks, such as storage device 3708. Volatile media includesdynamic memory, such as volatile storage 3706.

Common forms of computer-readable media include, for example, a floppydisk, a flexible disk, hard disk, magnetic tape, or any other magneticmedium, a CD-ROM, any other optical medium, punchcards, papertape, anyother physical medium with patterns of holes, a RAM, a PROM, an EPROM, aFLASH-EPROM, a flash drive, a memory card, any other memory chip orcartridge as described hereinafter, or any other medium from which acomputer can read.

Various forms of computer readable media may be involved in carrying oneor more sequences of one or more instructions to processor 3705 forexecution. For example, the instructions may initially be carried on amagnetic disk from a remote computer. Alternatively, a remote computercan load the instructions into its dynamic memory and send theinstructions over a telephone line using a modem. A modem local tocomputer system 3700 can receive the data on the telephone line and usean infra-red transmitter to convert the data to an infra-red signal. Aninfra-red detector can receive the data carried in the infra-red signaland appropriate circuitry can place the data on the data bus 3704. Thebus 3704 carries the data to the volatile storage 3706, from whichprocessor 3705 retrieves and executes the instructions. The instructionsreceived by the volatile memory 3706 may optionally be stored onpersistent storage device 3708 either before or after execution byprocessor 3705. The instructions may also be downloaded into thecomputer platform 3701 via Internet using a variety of network datacommunication protocols well known in the art.

The computer platform 3701 also includes a communication interface, suchas network interface card 3713 coupled to the data bus 3704.Communication interface 3713 provides a two-way data communicationcoupling to a network link 3714 that is coupled to a local network 3715.For example, communication interface 3713 may be an integrated servicesdigital network (ISDN) card or a modem to provide a data communicationconnection to a corresponding type of telephone line. As anotherexample, communication interface 3713 may be a local area networkinterface card (LAN NIC) to provide a data communication connection to acompatible LAN. Wireless links, such as well-known 802.11a, 802.11b,802.11g and Bluetooth may also used for network implementation. In anysuch implementation, communication interface 3713 sends and receiveselectrical, electromagnetic or optical signals that carry digital datastreams representing various types of information.

Network link 3713 typically provides data communication through one ormore networks to other network resources. For example, network link 3714may provide a connection through local network 3715 to a host computer3716, or a network storage/server 3717. Additionally or alternatively,the network link 3713 may connect through gateway/firewall 3717 to thewide-area or global network 3718, such as an Internet. Thus, thecomputer platform 3701 can access network resources located anywhere onthe Internet 3718, such as a remote network storage/server 3719. On theother hand, the computer platform 3701 may also be accessed by clientslocated anywhere on the local area network 3715 and/or the Internet3718. The network clients 3720 and 3721 may themselves be implementedbased on the computer platform similar to the platform 3701.

Local network 3715 and the Internet 3718 both use electrical,electromagnetic or optical signals that carry digital data streams. Thesignals through the various networks and the signals on network link3714 and through communication interface 3713, which carry the digitaldata to and from computer platform 3701, are exemplary forms of carrierwaves transporting the information.

Computer platform 3701 can send messages and receive data, includingprogram code, through the variety of network(s) including Internet 3718and LAN 3715, network link 3714 and communication interface 3713. In theInternet example, when the system 3701 acts as a network server, itmight transmit a requested code or data for an application programrunning on client(s) 3720 and/or 3721 through Internet 3718,gateway/firewall 3717, local area network 3715 and communicationinterface 3713. Similarly, it may receive code from other networkresources.

The received code may be executed by processor 3705 as it is received,and/or stored in persistent or volatile storage devices 3708 and 3706,respectively, or other non-volatile storage for later execution. In thismanner, computer system 3701 may obtain application code in the form ofa carrier wave.

It should be noted that the present invention is not limited to anyspecific firewall system. The inventive policy-based content processingsystem may be used in any of the three firewall operating modes andspecifically NAT, routed and transparent.

Finally, it should be understood that processes and techniques describedherein are not inherently related to any particular apparatus and may beimplemented by any suitable combination of components. Further, varioustypes of general purpose devices may be used in accordance with theteachings described herein. It may also prove advantageous to constructspecialized apparatus to perform the method steps described herein. Thepresent invention has been described in relation to particular examples,which are intended in all respects to be illustrative rather thanrestrictive. Those skilled in the art will appreciate that manydifferent combinations of hardware, software, and firmware will besuitable for practicing the present invention. For example, thedescribed software may be implemented in a wide variety of programmingor scripting languages, such as Assembler, C/C++, pert, shell, PHP,Java, etc.

Moreover, other implementations of the invention will be apparent tothose skilled in the art from consideration of the specification andpractice of the invention disclosed herein. Various aspects and/orcomponents of the described embodiments may be used singly or in anycombination in the computerized system having tiered data migrationfunctionality. It is intended that the specification and examples beconsidered as exemplary only, with a true scope and spirit of theinvention being indicated by the following claims and their equivalents.

The invention claimed is:
 1. A system comprising: a plurality of storagedevices; and one or more processors being operable to execute software,wherein the software comprises instructions executable to: manage astorage volume, the storage volume being operable to comprise a storagearea to which one or more tier areas of a higher tier of the pluralityof storage devices are allocated, manage a migration of data of thestorage area between the higher tier and a lower tier of the pluralityof storage devices, migrate uncompressed data of the storage area fromthe higher tier to the lower tier, compress the migrated data regardlessof an amount of used space of the lower tier, and store the compresseddata in the lower tier.
 2. The system according to claim 1: wherein thesoftware comprises instructions executable to decompress the compresseddata of the storage area, migrate the decompressed data of the storagearea from the lower tier to the higher tier, and store the migrated datain the higher tier.
 3. The system according to claim 1: wherein thestorage volume is a thin provisioned volume, to which a tier area of aplurality of tiers, including the higher tier and the lower tier, of theplurality of storage devices is allocated on a tier area basis inresponse to a write access from a computer to the storage volume.
 4. Anon-transitory computer-readable medium storing instructions that, whenexecuted by one or more processors, cause the one or more processors to:manage a storage volume, the storage volume being operable to comprise astorage area to which one or more tier areas of a higher tier of aplurality of storage devices are allocated, manage a migration of dataof the storage area between the higher tier and a lower tier of theplurality of storage devices, migrate uncompressed data of the storagearea from the higher tier to the lower tier, compress the migrated dataregardless of an amount of used space of the lower tier, and store thecompressed data in the lower tier.
 5. The non-transitorycomputer-readable medium according to claim 4, wherein the softwarecomprises instructions executable to decompress the compressed data ofthe storage area, migrate the decompressed data of the storage area fromthe lower tier to the higher tier, and store the migrated data in thehigher tier.
 6. The non-transitory computer-readable medium according toclaim 4, wherein the storage volume is a thin provisioned volume, towhich a tier area of a plurality of tiers, including the higher tier andthe lower tier, of the plurality of storage devices is allocated on atier area basis in response to a write access from a computer to thestorage volume.
 7. A method performed in a storage system having one ormore processors and a plurality of storage devices, the methodcomprising: managing a storage volume, the storage volume being operableto comprise a storage area to which one or more tier areas of a highertier of the plurality of storage devices are allocated, managing amigration of data of the storage area between the higher tier and alower tier of the plurality of storage devices, migrating uncompresseddata of the storage area from the higher tier to the lower tier,compressing the migrated data independently of whether an amount of usedspace of the lower tier exceeds a threshold, and storing the compresseddata in the lower tier.
 8. The method according to claim 7: wherein thesoftware comprises instructions executable to decompress the compresseddata of the storage area, migrate the decompressed data of the storagearea from the lower tier to the higher tier, and store the migrated datain the higher tier.
 9. The method according to claim 7: wherein thestorage volume is a thin provisioned volume, to which a tier area of aplurality of tiers, including the higher tier and the lower tier, of theplurality of storage devices is allocated on a tier area basis inresponse to a write access from a computer to the storage volume.
 10. Asystem comprising: a plurality of storage devices; and one or moreprocessors being operable to execute software, wherein the softwarecomprises instructions executable to: manage a storage volume, thestorage volume being operable to comprise a storage area to which one ormore tier areas of a lower tier of the plurality of storage devices areallocated, manage a migration of data of the storage area between thelower tier and a higher tier of the plurality of storage devices,decompress compressed data of the storage area, migrate the decompresseddata of the storage area from the lower tier to the higher tier, andstore the migrated data in the higher tier.
 11. The system according toclaim 10, wherein the software comprises instructions executable tomigrate the decompressed data of the storage area from the higher tierto the lower tier, compress the migrated data, and store the compresseddata in the lower tier.
 12. The system according to claim 10, whereinthe storage volume is a thin provisioned volume, to which a tier area ofa plurality of tiers, including the higher tier and the lower tier, ofthe plurality of storage devices is allocated on a tier area basis inresponse to a write access from a computer to the storage volume.
 13. Anon-transitory computer-readable medium storing instructions that, whenexecuted by one or more processors, cause the one or more processors to:manage a storage volume, the storage volume being operable to comprise astorage area to which one or more tier areas of a lower tier of aplurality of storage devices are allocated, manage a migration of dataof the storage area between the lower tier and a higher tier of theplurality of storage devices, decompress compressed data of the storagearea, migrate the decompressed data of the storage area from the lowertier to the higher tier, and store the migrated data in the higher tier.14. The non-transitory computer-readable medium according to claim 13,wherein the software comprises instructions executable to migrate thedecompressed data of the storage area from the higher tier to the lowertier, compress the migrated data, and store the compressed data in thelower tier.
 15. The non-transitory computer-readable medium according toclaim 13, wherein the storage volume is a thin provisioned volume, towhich a tier area of a plurality of tiers, including the higher tier andthe lower tier, of the plurality of storage devices is allocated on atier area basis in response to a write access from a computer to thestorage volume.
 16. A method performed in a storage system having one ormore processors and a plurality of storage devices, the methodcomprising: managing a storage volume, the storage volume being operableto comprise a storage area to which one or more tier areas of a lowertier of the plurality of storage devices are allocated, managing amigration of data of the storage area between the lower tier and ahigher tier of the plurality of storage devices, decompressingcompressed data of the storage area, migrating the decompressed data ofthe storage area from the lower tier to the higher tier, and storing themigrated data in the higher tier.
 17. The method according to claim 16,wherein the software comprises instructions executable to migrate thedecompressed data of the storage area from the higher tier to the lowertier, compress the migrated data, and store the compressed data in thelower tier.
 18. The method according to claim 16, wherein the storagevolume is a thin provisioned volume, to which a tier area of a pluralityof tiers, including the higher tier and the lower tier, of the pluralityof storage devices is allocated on a tier area basis in response to awrite access from a computer to the storage volume.